Irrigation by one means or another is necessary to grow agricultural products or to maintain landscape plants and lawns for a large portion of the United States. In 1986 sprinkler irrigation was employed for nearly 24 million acres of agricultural land in the United States and it remains the most common form of irrigation for lawns and landscaping. The introduction of relatively inexpensive control systems for sprinklers has resulted in the extensive use of automatic lawn and landscape sprinkling systems. While the automatic sprinkling system increases the ease of maintaining the lawn or landscaping, it also increases the problem of local flooding caused by missing sprinkler heads or broken sprinkler risers. Monitoring for sprinkler failures and repairing them is necessary to prevent the flooding and damage that could occur and adds an additional maintenance expense to the operation of a sprinkler irrigation system.
In a typical sprinkler irrigation system, main water supply pipes carry water throughout the system and individual sprinkler branches are distributed along the pipes. Each individual sprinkler branch consists of a riser and a sprinkler head. The riser, a short length of vertical pipe provided to elevate the sprinkler head to the desired level above the ground, is connected to the supply pipe by a tee, or an elbow, and the sprinkler head is attached to the top of the riser.
The flow of water out of a sprinkler head is limited by the design of the sprinkler when the sprinkler is operating normally, that is with the sprinkler head and the riser intact. In the event the sprinkler head is missing or the riser is broken, the water will flow out of the affected branch at a much higher rate. In addition to the potential flooding and damage to soil and crops caused by the excess flow, the remainder of the system will not function properly because of the flow lost to the damaged sprinkler. As a rule, the it is important to allow the debris to flush out through the device before putting the damaged sprinkler back in line. Then the system can be cleaned easily after a sprinkler break incident. The devices in the state of the art do not have such self-cleaning capability and they require a troublesome procedure to remove the debris once they fall in the piping through the break. This is one reason that the existing devices are not commonly adopted by the users.
Another crucial functional requirement for the shut-off device in a sprinkler irrigation system is the need to differentiate between the high transient flow surges normally experienced during start-up and the high flow due to a break in the sprinkler branch. These flow surges, which quite often exceed the threshold flow, are caused by air which has entered the irrigation piping while the system was off. The air, which replaces the water normally present during operation, can flow out of the sprinkler head at a higher volumetric rate than can the water it is replacing and the flow surges until the air is discharged. The automatic shut-off device must not actuate as a result of this flow surge.
The design of the disclosed device takes advantage of the difference between these surges and a broken sprinkler branch. During the start-up of a sprinkler irrigation system there may be several flow surges, each of very short duration. The difference between the flow surges and the broken sprinkler branch is the transient nature of the flow surges. Flow from a broken sprinkler branch increases above the threshold are remains there indefinitely, whereas the flow during start-up may increase above the flow threshold but almost immediately returns to nearly normal flow rates.
The disclosed device includes a damping mechanism incorporated in the shut-off device which delays the action of the shut-off mechanism and prevents the temporary flow surges from actuating the shut-off mechanism, thereby allowing the system to start up normally. At the same time, the delay action of valve closure can service for the self-cleaning purpose which allows the trapped debris to pass through before the water is stopped. There are shut-off devices which utilize some form of damping mechanism, for example, the device described in U.S. Pat. No. 3,735,777. However the damping mechanism has been included for a different purpose, namely for mitigating the "water hammer" effect which would result form an abrupt closure of the shut-off device. Cleaning debris and by-passing start-up surges requires a much longer closure time than is required to mitigate the water hammer.